Math 3c, and Nitrogen, 2023, part 2

What is nitrogen, and how to warehouse it, when it’s in liquid form (Part 2 of 2).

Uses of liquid nitrogen differ from uses of it in gas form. We are focusing on the first mentioned state of aggregation. It is used first and foremost to keep various goods cold and it is a refrigerant of raw materials, medicines, food products, etc. In laboratories, nitrogen in liquid form is used to cool chemical reactions, for testing electronic devices, shrink fitting (which is joining for example metallic parts together during an installation) and in other areas this is used for pipe freezing. We are going to explain all these 4 latter uses. Liquid nitrogen is nontoxic and noncorrosive, but the dangers with it are that you can get oxygen deficiency or get frostbite, because what’s inside this coolant technology is of such extremely low temperature. Liquid nitrogen and liquid carbon dioxide are used in the cryogenic cooling technology where they have many advantages compared with mechanically cooled systems. The last one has many different components which makes it both heavy and complicated.

In case of changed planning and redecoration at the laboratory, it does not cost so much to relocate a vacuum insulated tube compared with moving a freezer, compressor, heat exchanger rewinds, ventilators and many other things included. Chilling mechanically is also not as effective as using N2-gas, and you can only get down to above -55 C with the first mentioned. With an oxygen monitor on the wall and an alarming system you and your staff are very safe while handling liquid nitrogen, that is held together in pairs with triple bonding, that require large amounts of energy if you want to try to break them up. But the intermolecular bonding is instead being held together with van der Waals bindings, because of temporary delta minus and plus charges on two poles. The reason is that electrons are never still, and sometimes they are both in the same place on the diatomic molecule in question (same with other nonpolar molecules). In such moments, van der Waals arises.

The molecules influence each other a lot to form such bonds in question. A temporary positive pole brings out a temporary negative pole in someone else. This is how they function, and it is incorrect to claim that van der Waals bindings between molecules are always weak. Hydrocarbons teach us that the longer the chain, and the more van der Waals bonds there are, the higher the boiling point. The alkane (where there are only single bonds between the carbons) decane, C10H22, has a boiling point on 174 C, with its van der Waals bindings. But let’s go back to the diatomic molecule N2. It can be used in a fire suppression system because it’s reducing the oxygen which will put out the fire. No byproducts will be produced during that and N2 itself will not rot. In laboratories it can cool down many chemical reactions the same way. Also, let’s not forget the scientist’s tool that is called cryo-EM, when you prepare samples of any kind or illustrate protein or chemical compound patterns.  

Cryo-EM technology allows you to see proteins in a sharp image, because one effectively freezes them in a thin layer of liquid and then observes them. It’s not like with the X-ray that proteins must lie still and be tightly packed in a crystal structure, otherwise your image will be completely blurred. Same thing with gases, sometimes you want the ethane gas to become a liquid for various reasons, for example during a study on the molecules in the lab. Then you use the liquid N2 on the C2H6 gas. Now we will explain that part about testing electric devices with the help of N2. NASA (the Space Administration) tests a lot if their machines and metals can withstand extreme cold, but you can test the endurance of many different devices as well. In an environmental chamber you can observe if the company’s industrial products or materials tolerate for example a lot of moisture, if the material will hold if it’s exposed to salt, or if it can withstand extreme temperature fluctuations? (N2 is used here).

Shrink fitting with N2. This is when you have metal parts that you either want to put together or separate from each other. You first need to heat them to between 150-300 Celsius, and when the metal has expanded then you relocate the parts with your equipment, and when it’s done you cool the device down with a lot with liquid nitrogen. The metals will then contract by the huge temperature change and sit together in a new way (if that was the goal), and then they are shrink fitted thanks to thermal (heat-related) expansion. With N2 you can also do pipe freezing, which is when you want to create a solid plug of the liquid inside a pipe, so the activity inside becomes still. That allows you to modify the pipe on one side or to pressure test the pipe. N2 cools down an optional small part of the tube from the outside (you put on a fit freeze jacket). Remember to always wear protective glasses, and gloves (preferably a little too large, so you can pull these off quickly).